Suppose  \vec{G} is a vector field with the property that  div\vec{G} = 5 for 2 \leq ||\vec{r}|| \leq 14 and that the flux of  \vec{G} through the sphere of radius 4 centered at the origin is  20\pi. Find the flux of through the sphere of radius 12 centered at the origin.

I am really confused on where to start at this point